This invention pertains to computers and other information handling systems and, more particularly, to a power supply system for use with hot pluggable adapter cards in which a circuit averages the voltages at the power supply pins of the active I/O bus connectors to regulate the output voltage of the power supply, and in which the feedback voltage from the power supply pins of the I/O connectors to the input port of the power supply is switched ON or OFF at appropriate times.
FIG. 1 is a schematic diagram of a prior art computer system. Referring to this figure, power supply 101 is a well known power supply having a voltage output port Vout, a ground terminal GND, and two input ports Vsense+ and Vsense- for receiving a sense voltage that controls the voltage at the output port Vout. A resistor 102 and series connected FET switch 103 having a control input 103a are connected to the positive power supply pin 104a of a well known I/O bus connector 104, to which a well known adapter card can be attached. In the typical prior art system, more than one I/O connector is usually included and connected to power supply 101 in a manner similar to that of connector 104. The negative power supply pin 104b of connector 104 is connected to ground. The two terminals of the "current sensing" resistor 102 are connected to two Isense input terminals of a well known hot plug controller 105. The voltage drop across resistor 102 is proportional to the power supply current flowing into the adapter card plugged into connector 104 and this voltage drop can be used by hot plug controller 105 to sense the presence of an adapter card in the "slot", and to provide over current protection. The power supply voltage at pin 104a is connected to a Vsense input of hot plug controller 105. A control output port of hot plug controller 105 is connected to the control input 103a of switch 103 and turns the switch OFF just before an adapter card is plugged into or removed from connector 104, and turns the switch ON just after the adapter card is plugged into the slot.
While the prior art power supply system may work well when only one adapter card is connected to the I/O bus, unacceptable variations in the power supply voltage at the power supply pins of the various I/O connectors in the system can result, particularly if there is a significant difference in the power consumed by the various adapter cards. These unacceptable variations in power supply voltage can be deviations from the ideal or "spec" power supply voltage, as well as variations in the power supply voltage from one adapter card to the next. Accordingly, the invention described below regulates the power supply voltage such that the average voltage at the power supply pins of the active I/O connectors is within close tolerances of "spec", and such that the deviation of the power supply voltage at any one I/O connector from spec is minimal.